The Peres conjecture is false: One of the most famous problems in quantum information physics solved

November 5, 2014

Since 1999, the conjecture by Asher Peres, who invented quantum teleportation, has piqued the interest of many scientists in the field. According to his hypothesis, the weakest form of quantum entanglement can never result in the strongest manifestation of the phenomenon. Today, a team of researchers from the University of Geneva (UNIGE), Switzerland, and the Hungarian Academy of Sciences have proven this conjecture to be false, thus solving one of the most famous problems in quantum information physics. This news was published in Nature Communications review.

The physicist Asher Peres was very interested in the phenomenon of quantum and its different manifestations. When two objects (take photons, for example) are entangled, they remain correlated regardless of the distance that separates them physically: whether they are separated by a millimetre or by several kilometres, any action done to one of them will immediately affect the other. To check whether a system is entangled, scientists test for Bell's inequality. If the experimental measurements violate Bell's inequality, this means that the two objects are entangled, and that they correspond to two manifestations, in different locations, of the same single object. This is called nonlocality.

A Problematic Conjecture

In 1999, Asher Peres conjectured that the weakest form of an entanglement will never result in the strongest manifestation of the phenomenon. Explanations.

The violation of Bell's inequality represents the strongest form of entanglement. Two objects must indeed be strongly entangled in order for the system's experimental measurements to violate Bell's inequality. On the other hand, there also exist states with very weak entanglement. Asher Peres wondered if it would be possible to distil several wealky entangled states in order to make a strongly entangled one, as one would distil alcohol. The theory showed that this was possible, but not in every case. Certain states are in fact too weakly entangled to be distilled; this is the case of bound entanglement, which is considered the weakest form of the phenomenon. Peres therefore concluded that the weakest form of entanglement could never result in the strongest manifestation of the , namely nonlocality.

Later, a number of scientists tried to prove his conjecture. Some succeeded in a few particular cases, but none were able to demonstrate the claim in general. Peres's conjecture was therefore considered to be one of the most famous unresolved problems in the field of quantum information physics... until now. In fact, Nicolas Brunner, a physics Professor at UNIGE's Faculty of science, and Tamas Vertesi, a researcher at the Hungarian Academy of Sciences, were able to disprove Peres's conjecture. "To do so, we just had to find a counter-example," explains Professor Brunner. "Using numerical algorithms, we showed that a bound entanglement can violate Bell's inequality, without needing to be distilled."

Explore further: Quantum physicists shed new light on relation between entanglement and nonlocality

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13 comments

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edseds727
5 / 5 (4) Nov 05, 2014
What an incredibly exciting to be a young person majoring in physics. I wish I could be 17 years old again.
mikep608
1 / 5 (7) Nov 05, 2014
HERE'S MY WEBPAGE LINK. I LIKE TO REINTERPRET EXPERIMENTAL RESULTS BECAUSE I CAN. AREN'T ATOMS A FORM OF PROTONS AND ELECTRONS HAVING QUANTUM ENTANGLEMENT? IT'S NOT SUCH A STRANGE PHENOMENON.

https://www.faceb...timeline
phaseshifter
3.5 / 5 (2) Nov 05, 2014
"When two objects (take photons, for example) are entangled... any action done to one of them will immediately affect the other."

This is completely wrong, and is exactly the spiel used to make homeopathy (and other pseudosciences) sound (to the uneducated) like it has a credible base in physics.
jdavis417
1.2 / 5 (6) Nov 06, 2014
Since the mechanism of "entanglement" seems to be unexplained, is it okay to just say that they communicate via dark energy transmitted through dark matter? ;)
AmritSorli
1 / 5 (2) Nov 06, 2014
quantum entanglement is immediate and carried directly by the space in which time is noth 4th physical dimension but only duration of motion.
http://www.degruy...14-5.xml
teenagewasteland
1 / 5 (2) Nov 06, 2014
one can liken the entanglement phenomenon to other systems of simultaneousness. like a see-saw. push on one side and no signal needs to take place. both sides change immediately or instantaneously or simultaneously. the see-saw example means the things measured change in respect to position. as in quantum entanglement the amount one is changed the other changes simultaneously. push one down a foot and the other one goes up a foot. instantaneously. the see-saw is what the confusion is all about. we see and measure the things on the see-saw but not the see-saw itself.
shavera
5 / 5 (2) Nov 06, 2014
actual physics of entanglement: If we assume that quantum measurements have no "hidden" variable that truly is deterministic, *and* we assume that even such hidden variables cannot transmit their information faster than light... we would expect results *different* from what we observe. Therefore either
A) there aren't hidden variables informing a particle how it "truly" is (quantum mechanics is truly random)
or
B) physics must allow for non-local, ie faster than light, processes.

The standard interpretation is to take A. Quantum particles are truly indeterminate. This means nothing at all is transmitted faster than light.

But it also means that an *entangled* system of particles has more information than either one of the particles carries alone. It's not that one particle changes the other particle by some voodoo magic. It's that you need to know BOTH particles' measurements to extract the system's information.
teenagewasteland
1 / 5 (1) Nov 06, 2014
and i dont think the device that connects the entangled things exists in a different dimension or parallel universe or whatever. its just a different field that occurs when conditions are right. a cake doesnt always exist but exists when the proper ingredients are combined and cooked. anyway there is no signal being sent from one affected photon to the other affected photon. what is affected is the field/see-saw that the photons got onto upon being connected.
antialias_physorg
5 / 5 (3) Nov 06, 2014
Information is the correlation between encoded and decoded state.

In entanglement you do not have an encoded state (you can't 'set' the particle to any specific state beforehand, because this would be an interaction/measurement and break any entaglement).
So while entanglement may seem non-local the measurement of the entangled entites does not constitute information transmission (and hence particularly not FTL information transmission).

There's a reason why it's called "(spooky) action at a distance" and not "information transmission at a distance"
phaseshifter
5 / 5 (1) Nov 06, 2014


The standard interpretation is to take A. Quantum particles are truly indeterminate. This means nothing at all is transmitted faster than light.

But it also means that an *entangled* system of particles has more information than either one of the particles carries alone. It's not that one particle changes the other particle by some voodoo magic. It's that you need to know BOTH particles' measurements to extract the system's information.

Exactly. Entanglement relies on knowing a property of the system as a whole (i.e. total spin angular momentum).

Observing that property for one particle (by observing the spin, for instance) determines that property for the other particle. The only events exhibiting nonlocal effects are measurements of the correlated properties. Properties unrelated to the correlation will not exhibit nonlocal effects, and attempts to manipulate (rather than observe) the correlated property will break the correlation.
Da Schneib
not rated yet Nov 07, 2014
actual physics of entanglement: If we assume that quantum measurements have no "hidden" variable that truly is deterministic, *and* we assume that even such hidden variables cannot transmit their information faster than light... we would expect results *different* from what we observe. Therefore either
A) there aren't hidden variables informing a particle how it "truly" is (quantum mechanics is truly random)
or
B) physics must allow for non-local, ie faster than light, processes.
Bell's Theorem says it must be one or the other; either non-locality or contrafactual realism. Nice analysis.
Da Schneib
5 / 5 (1) Nov 07, 2014
Information is the correlation between encoded and decoded state.

In entanglement you do not have an encoded state (you can't 'set' the particle to any specific state beforehand, because this would be an interaction/measurement and break any entaglement).
So while entanglement may seem non-local the measurement of the entangled entites does not constitute information transmission (and hence particularly not FTL information transmission).

There's a reason why it's called "(spooky) action at a distance" and not "information transmission at a distance"
What we know for sure is that it's *either* information transmission at a distance, i.e. non-locality, or that particles in superposition actually don't have any value of the superposed variable, i.e. contrafactual definiteness. But we have not yet devised an experiment to determine which (and Bell's Theorem says we never can).
russell_russell
not rated yet Nov 22, 2014
This is an honest question.

The label "action" is used in this thread commentary.
Is this "action" kinematics (the study of motion) or dynamics (the study of forces) or neither?

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